The meanings of modal verbs are extremely important for understanding how modal verbs work. This or that modal verb in one of its meanings can't form the past tense; in another meaning it is used only with a negative; in still another meaning it can't form a question or, on the contrary, is used only in the form of a question.
The meanings of modal verbs are created by the context and by the grammatical structures in which they are used. If the context is not clear enough, it may be difficult to understand in which meaning a modal verb is used. For example, look at this sentence: "You must speak English." Does it mean "You have to speak English" or "You probably speak English"? We need more context to say for sure, for example, "You must speak English at the conference" (strong necessity) or "You have lived in Canada for several years, you must speak English" (strong probability).
Certain grammatical structures also provide additional context and help us choose the right meaning of a modal verb. For example, quite often the use of the infinitive BE after certain modal verbs is an indication that the meaning is "probability, possibility".
He must be rich.
They may be at home.
She could be sleeping now.
The meanings of modal verbs are a little difficult to single out and define clearly (especially if we try to define them in Russian). For example, when speaking about the main meaning of the verb CAN, some linguists use the words "ability, possibility", others speak about "physical and mental ability", still others say "ability, power, skill, opportunity". The material Overview of Modal Verbs describes the meanings of modal verbs in general, and typical examples of use are given. The materials on specific modal verbs describe their meanings, usage, and peculiarities in detail. Specific modal verbs are grouped by their meaning in the materials of this section, e.g., Ability, Advice, Necessity.
Will/ Shall (would/should)
We use will when we decide to do something at the time of speaking:
Oh, Iíve left the door open. Iíll go and shut it.
ĎDid you phone Lucy?í ĎOh no, I forgot. Iíll phone her tomorrow.í
We use will in the following situations:
Offering to do something
That bag looks heavy. Iíll help you with it.
Agreeing to do something
A: Can you give Tim this book?
B: Sure, Iíll give it to him when I see him this afternoon.
Promising to do something
ĎCan you give me the money? Iíll pay you back on Friday.í
Asking somebody to do something
Will you please turn the radio down? Iím trying to concentrate.
Shall is used mostly in the questions shall I Ö? / shall weÖ? to ask somebodyís opinion (especially in offers and suggestions):
Shall I open the window?
Shall we go now?
We use would/wouldnít when we imagine a situation or action (we think of something that is not real):
It would be nice to buy a new car, but we canít afford it.
Iíd love to live by the sea.
Should is used to give an advice or to give an opinion: